Racket and art of manufacture thereof



I Aug. 28,1928.

- H. W. HALL RACKET AND ART .OF MANUFACTURE THEREOF s Sheets-Sheet 2 Filed Nov. 21. 1925 7 w I l 6 juxafiibr race ldHa l E Aug. 2a, 1928.

' H. W. HALL RACKET AND ART OF MANUFACTURE THEREOF Filed Nov. '21, 1925 3 Sheets-Shegt 3 orac'eldfla El WJW Patented Aug. 28, 1928.

UNITED STATES HORACE W. HALL, OF NEWTON CENTER, MASSACHUSETTS.

RAOKET AND ART OF MANUFACTURE THEREOF.

Application filed November 21, 1925.

This invention relates to improvements in rackets and art of manufacture thereof. More particularly it relates to the racket frame, for'whicli it provides a combination of strength, lightness and balance hitherto impossible in a frame made of wood. It also provides a process for mass production of high grade rackets of standardized design without requiring such special selection of wood and such special skill of workmen as are now necessary for high quality product. For these reasons and also because it reduces the number of operations in manufacture, it provides reduction of cost of manufacture, and an improved product with incidental other advantages, among which are the possibility of tighter stringing, and the prevention of warping.

The game of lawn tennis has developed to such a degree that before this invention thedemands of skilled players for strength of frame, coupled with balance, lightness, speed and durability, could not be satisfied by any rackets which the world has known how to make, not even by the most expensive, so far as I am aware. The making of a racket thoroughly satisfactory in any one of the above respects could be accomplished only by sacrifice of some other desired quality. And there would always be danger that the frame would warp out of the true plane form which is necessary for accurate play.

Although rackets for the game of tennis are more especially mentioned herein, the benefits of the invention are not limited to that particular variety of racket, and in some respects they are applicable to other wood:

products.

The invention employs untreated natural stock, preferably of suitably porous wood. slash sawn or cut from the log; and may use native white or gray oak which have hitherto been deemed less suitable because of weight and brittleness, an d poplar or spruce hitherto thought too weak. And whereas lightness of the head, necessary for balance, has hitherto been obtained by shaving that part. .of the frame to smaller size, the present invention makes it possible to retain the larger crosssectional dimensions which are sacrified in present standard rackets. The needed lightness is obtained by the use of light, less dense wood. Per se this is weaker than the selected ash customarily chosen; but the needed strength is acquired, and exceeded, by choos ing a kind of light wood which is porous;

Serial No. 70,530.

using it in thin laminae which are capable of being bent, untreated, to racket shape without retaining any important internal stress from such a bending; and gluing the porous lamina together with ample absorption of glue into the pores, producing a grid of stiff colloidal webs of glue. It is also a feature, valuable in getting best results, to use groups of laminae that were cut all from the same log, but rearranged so as to be mutually reversed, with the grain all longitudinal, producing a weaving of the grain as I call it. Also I combine with the lighter wood laminae a few laminae of strong wood, at the surfaces, where wear of tight strings will come. The result is a composite structure with a resultant of physical properties quite different from those of the component woods in the structure, and different from what the bow would'be if made solid of either component variety, but having the desired physical and mechanical properties for a strong, light, non-warping tennis racket how such as has heretofore never been produced in wood. The composite structure may contain only four or five laminae of ash, for example, with seven or eight laminae of yellow poplar, basswood, or spruce between them, all of which can be bent and set at one operation with the setting of the throat piece and handle plug. The simultaneity of the flexing of laminae and of their lubrication by glue, and proper compression on each other and on the throat piece, maintained while the glue sets, makes an automatic perfection of fit to the throat piece and an economy in'manufacture which are new and valuable. This operation is expeditiously performed by apparatus for holding, bending and pressing wherein the grouped broad sheet laminae, wide enough to make a dozen or so rackets, stand together on edge while being bent around a caul having the shape of the head of the racket and {compressed inward perpendicularly against it from all directions. This caul is in two parts each having 'a continuous face from throat to tip, and has a. wedge part at the tip of the racket head which spreads the said two parts to full head shape, and whose removal when the glue has set allows contraction of these two parts for release o the bowed composite sheet. This how sheet being then slit into sections of proper width, individual frames result, in form to be finished and strung in the usual way.

The finished bow is so light, compared with bows of previous rackets of equal size, that the shaving hitherto necessary to reduce weight of head, for proper balance, can be omitted so that the wood around the head retains its practically rectangular cross section, with full dimensions. The lighter wood, which makes the great part of the ulk, may have only sixty per centof the weight a stick of ash of equal size would have, as 1n rackets made hitherto. But it may at the same time have eighty per cent of the strength of ash. When subjected to a bending stress like that imposed upon a racket in severe play, the stiffness of a stick varies as the cube of its depth in the direction of stress; and its breaking strength varies as the squarepf the depth; but the weight varies directly with the depth. Thus the providing of the racket bow with large cross-sectional dimension from face to face of the racket adds to its strength and stiffness more than it adds weight.

Moreover, a well made glued joint between";

suitably porous woods is stronger than the wood itself; and a light wood as poplar, bass or spruce takes a stronger glue joint than ash, or other dense wood. This increases the relative strength of the poplar bass or spruce, especially because in the racket of the invention each web of the hardened glue, stronger I than any wood commercially used, reinforces the light wood like steel in concrete. Also, the grid of stiff webs extending through the midst of the wood in the direction of stress in play, adds strength and stiffness to the whole as does the web of steel in an I-beam while adding little weight and no appreciable thickness to that of the wood.

By this low-cost process of manufacture, with preservation of the native cell structure of the wood by avoiding the customary boiling or steaming processes, the composite product attains a surpassing strength coupled with lightness; a stiffness in the plane of the head that renders the very tightest of stringing feasible; a hardness to resist the wear of gut; and a durability which prevents warping with lapse of time. And because of the uniformity or averaging of grain automatically produced by the longitudinal weaving of the grain, and the automaticperfection of the joints between laminae and throat piece, it is possible to use this process for mass production of racket frames of uniformly high uality without that needfor individual selection of stock and that high degree of skill of workman which has hitherto been necessary for the making of high quality rackets.

Other details and advantages will appear from the description which follows. It is intended that the patent shall cover by suitable expression in the appended claims, whatever features of patentable novelty exist in the invention disclosed. The invention is not limited to the particular details and apparatus herein set forth, but the accompanying drawings illustrate one way of practicing the invention:

Figure 1 represents four laminae or sheets of veneer to be used in making a dozen or so rackets, arranged in their relations to each other as they existed in a log;

Figure 2 represents a preferred re-arrangcment of the same for weaving of grain;

Figure 3 represents several such groups of laminae assembled to make a single composite sheet;

" Figure t represents the composite sheet formed into and set in the shape of the racket; arrows indicate places and direction for application of pressure, and order of application, for bending the sheet from the plane form of Figure 3 to the bow sheet in racket form of Figure 4;

Figure 5 represents the sub-division into frames for individual rackets;

Figure 6 represents a completed racket;

Figure 7 is an edge elevation of a portion of this racket;

Figure 8 is a plan of apparatus for'bending thecomposite sheets of Figure 3 to the form of Figure 4 and setting them with glue, with simultaneous fitting and setting of the throat piece;

Figure 9 is an end elevation of the same in section on line 9-9 of Figure 8.

Referring to the drawings, 10 indicates a group of four laminae or sheets of veneer, a, b, c and d, of requisite size, for example ten inches wide and each thin enough to be bent easily to racket shape, preferably each about one-twentieth of an inch thick. These may have been slash cut or sawn, by suitable veneer cutting machinery of a nature already well known, from a log in which they lay as represented in Figure 1, where the direction of the grain of the wood with reference to the plane of cutting is represented at 11, although of rather exaggerated obliquity. Comparison of this with Figure 2 shows the reversals of these sheets which may be made for the assembly shown at 14, Figure 3, to produce the arrangement which I herein for convenience call a longitudinal weaving of grain. These are arranged with the grain of each running in the general longitudinal direction of all of the sheets, but with the several sheets mutually reversal -side by side, or end for end, or both,from the positions which these sheetsoecupy with respect to each other in the log from which the veneer was cut. The departures of grain direction from strict longitudinality are utilized to increase the strength of the bow. Such departures are always present in wood having grain running nominally longitudinally, owing to the way the veneer is cut from the log; and in a single sheet they are elements of weakness and are especially dangerous because the grain may dip rather sharply across the sheet and because it is extremely difficult to see how the grain really lies. By observing the direction of the obliquity of the grain on the edges of the sheets, and the nearness or remoteness of the pictured points of the flower of the wood on the sides of the sheets, in the different parts of Figure 2, this particular embodiment of a preferred arrangement can be analyzed. In this case the sheet a remains as in Figure 1; sheet 6 is reversed side for side, that face which was upward being downward, and the angle of the grain being equal and opposite to that of sheet a; sheet 0 is reversed end for end, and side for side, that face which was upward becoming downward; and sheet 03 is reversed end for end, that face which was upward remaining upward. The reversals of obliquity, toward right and left, and toward front and back of the composite sheet, produce. an internally opposed arrangement of cleavages that makes breakage more difficult. They produce a balancing or neutralizing, however the grain may lie. By the thin cutting of the log each obliquity of grain (as for example, where the grain veers upward and to the right across the plane of cutting) becomes sectioned into four; and the subsequent mutual reversal of these makes the irregularity balanced against itself and also distributes it throughout the group of sheets so that the effect of the. irregularity is diminished. Yet the same general direction of grain is preserved. When made into a racket the grain runs around the bow in every lamina, not across the bow in any case; but the reversals apply themselves automatically to every cross grain running obliquely between inside and outside of the bow, across the thin dimension of the sheets, as well as to the variations of grain direction from strict parallelism with the faces of the racket. It might be said that each-weakness is thus averaged with the rest of the wood; but the process goes further for the distributed parts are to an extent opposed to each other, so that the irregularity which in a single sheet constitutes weakness is neutralized by its own practical reversals; and the combination gives a final product of very perfect uniformity and great strength as compared with a bow made integrally of a selected grade of the same wood as hitherto commercially practiced.

This longitudinal weaving also stabilizes the racket against warping. The tendency of any individual ply to warp in a particular way is resisted by equal and opposite tendency in another, reducing also the tendency to twist which so often occurs in a. solid ash stick. These reversals also make for uniform density through the length and breadth of the composite structure, so that in general no part of the frame is stronger or weaker than any other part. On account of the additional strength and stiffness developed it is possible to gain lightness by making the finished frame in smaller cross section than heretofore, entirely of a strong wood, as ash, and yet to have better results than in the integral ash frames at present commonly used. lint the method to gain lightness by substituting lighter wood for some of the lamina is prcferred because the resultant makes a stronger and stiffer bow for its weight than a multiply bow made all of ash and thinned down to lightness. To produce this interweaving it is not necessary that sheets be used which were in absolutely contiguous positions in the log. nor even from the same log, nor in the same order above described for illustration, but this will ordinarily produce most perfect balance.

In the preferred process of manufacture the cut veneer may be air dried for a short time (but preferably is not kiln dried which weakens the wood structure) so as to surface dry the stock and render it fit for gluing. The veneer is cut not thicker than one-sixteenth of an inch if dense wood, or oneeighth if light, as poplar, but preferably onetwentieth, in order to be thin enough to bend well; and any width of veneer can be utilized from six inches up to twelve or fourteen, so that the entire product of the log can be used without-waste. Choosing for example ash respectively for the three outer laminae a,

a, (r, of Figure (3, and for the inner lamina 1/, i

and poplar for the intervening lamimc 0; these may be arranged for weaving of grain and suitably coated with casein or other glue, assembled and bent as a single multi-ply group sheet, to make a thickness equal to that; which is desired for the maximum thickness of the rough racket frame, measured from inside to outside of the frame. An impor tant feature is the inserting and gluing in of the throat piece 50 and the handle plug 51 at the same time when the bow itself is made. This is not possible when wood has been steamed for bending or is bent green and full of water. for such sticks are bent in a wet, soft condition and allowed to dry and take their permanent set before inserting the throat piece which is glued to the bow stick. But by the present invention the laminae are in perfect shape to be glued to the throat piece and handle plug at the same time as they are glued to each other. All internal stresses are practically eliminated. Owing to the adaptability of the wood at the time of gluing. the glue joint between the throat piece and the bow part is secure, for the application of the bow to the throat piece when all the veneers are soft and flexible makes aperfect fit under moderate pressure. It becomes possible, moreover, to standardize the. shape and size of the throat piece 50 and too make this element in multiple identical numbers, as compared with the present need of marking each and cutting it on a jig saw and making individual fittings owing to the fact that the solid stick steamed bows twist in drying and Oll lll

thus necessitate individual fitting as well as resulting in a glue joint which is either very expensive or is in danger of being insecure.

The laminae may comprise for instance .welve plies of one-twentieth in'ch each, assembled as in Figure 3, and transferred to the apparatus which is to bend them to racket shape, as for example that shown in Figures 8 and 9, which is to bend them from the shape if Figure 3 to that of Figure 4. The pressure is made to center at the middle laminae of the bow and is applied with substantial uniformity and perpendicularity over the surfaces which are under compression, that 's, to the curve of the ultimate shape. The pressure may be applied by sectional cast- 1ron cauls 48, in the design of which the thickness and faces may be shaped while taking account of the yielding of which the iron is :usceptible as pressure increases, so that an intensity of to 100 pounds per square inch normal to the surface can be produced all over the working face of the sectional caul by screws 58 or other pressure means applied It a limited number of points, e. g. at the points of these screws in the middle part of the caul. The group of laminae is first compressed at the middle "of its extent, as at 1 in Figure 4, where the tip of the racket head s to be; and then, by compression applied to it at points progressively further from this center in each direction toward the end of the group, indicated diagrammatically at 2, 3, 4, 5, 6, 7 and 8 the group sheet is bent from plane into frame shape. In so doing the bow curvature is gradually produced, without the impounding of air or thick bodies of glue between the laminae and without placing the laminae under tension. This is because during this stage of the process the ends of each sheet remain constantly free to move; and when the point of application of pressure moves from the centre toward the ends of the group eachsheet can slip on its neighbors to adjust itself to the new curvatures to which it is successively constrained. At each point the curvature is slightly difierent on each sheet from that of the neighboring sheets at the same point of compression, so that, by the separation of the bow into sheets at this place of curvature, the severe strain which always results in the bending of a thick integral stick to that curvature is eliminated, because the thin sheets are individually free to assume the position where the curvature imposes least stress. The slippage produces a spreading longitudinally of the several parts of any defect which existed in the original log. Assuming such a defect to have been large enough to pass through several laminae, thefragments thereof found in the'first, fifth, ninth. etc. laminae might remain concentrated together in their original positions after the above reversals. But, by the slippage, each such defect may be moved enough, automatically, to bring it opposite a sound part of the correspondingly defective adjacent laminae. This further increases the probability that the resulting product will not be seriously affected by the existence, initially, of such a defect. And it permits lower grade or less well selected stock to be used with good results.

The apparatus illustrated for executing this stage of the process, gluing the throat at the same time, has a central caul in two halves, 24, supplemented by a wedge element 28 for spreading them, with a range of straps 62 and screws 64, 58 around, pressing on head caul 65 and other exterior cauls 48. The apparatus illustrated in Figures 8 and 9 has legs 22 adapted to stand on a bench or other support as, for example, on a. pair of horizontal supporting bars 20, in which case each leg may carry a rigid collar 23 near its lower end to rest on the supporting rack 20 while the leg itself projects down a little through a hole therein. These legs 22, and other upri hts 22, which do not reach down so far as to e legs, rise as parts ofthe inside cauls 24 and project upward above them to be engaged by straps 62 which link together the inside and outside cauls. The top of the throat piece 50 is represented as having a wooden covering strip 26 which may be glued to the end of the throat piece 50 by the same operation. The wedge caul 28 may have a slight taper so that when moved toward the racket tip by driving it to the position illustrated in Figure 8 it will spread the side cauls 24 to their compressing position, illustrated, i. e., to the limit permitted by the slots in cross-ties 34, making a surface continuous for the complete circuit of the inside of the racket head; and, so that when it is knocked inward it allows a slight collapsing of the side cauls 24, inward, for clearance for removal of the completed and then rigid racket frame. At the throat the two side cauls 24 have a bearing together 29, on which they rock slightly as they collapse at the tip under influence of the cross spring 36 which tends to contact these cauls. The

tip caul 28 may rest down loosely and movably 'ects under it from one of the uprights 22 or 22 and has a pivotal connection 54 to an outside upright bar 56 havinv suitable compression devices 58 adapted to bear inward against an outside caul 48 and the outside upright is pivoted at the top at 60, to a top strap 62 which loops around an upri ht 22 or 22' of the inner caul 24. Preferab y the exterior cauls are made of resilient metal, for which cast iron properly sha ed will serve, so that as pressure is applied t e'end portions of the caul first engage the laminae, and are then bent backward with further screw pressure, until the middle of the caul engages. In this way the whole area may get approximately its proper pressure per square inch, for example a pressure approaching 100 pounds per square inch, applied perpendicularly to its surface and with the center of compression approximately coinciding with the center of the group of laminae under pressure by the particular cooperating cauls.

In the operation of the apparatus illustrated in Figure 8 the loops 62 and outside uprights 56 are all to bethrown back on their pivots 54 and 60. This leaves the rigid straps 52 underneath exposed as a support on which the composite assembly of thin sheets 14 can be placed on edge and held by gravity until they are held by compression. Upon throwing'up the loop 62 at the tip and engaging it over the caul 28 and setting up the screws 64 or whatever other means is provided for strong and quick compression the outside caul 65 at the tip is compressed strongly against both the inside narrow caul 28 and the adjacent parts of the inside cauls 24, due to the shoulders 28, thus making the pressure uniform over the entire area of the outside head caul 65. Then in turn the outside cauls 48 on each side of the head may be applied, by screws 58, thus bending the sheets without placing them under any tension, and simul taneously expelling all air, so that a tight joint results. The last of the cauls 48 are shaped and extended so as to cover part of the handle and part of the head in the region of the throat piece 50, against which the inside cauls 24 bear through the intervening plate of wood 26. The assembly of the throat piece with the frame at the time the frame is bent and fixed in its permanent shape is a new accomplishment, so far as I am aware. It has the great advantage of making a right lit and a secure joint with little effort and with a saving of one rather troublesome operation. As this is done with veneer sheets all in a state of fiexibilty and lubrication the bow can easily adjust itself to the exact curvature in which the throat piece may happen to have been prepared. This is without the stress of wood experienced if a full thickness of stifi frame had to be bent to make such adjustment; and makes a joint that is free from the severe stress that would always tend to open. the joint under such conditions. Moreover, the throat can be made of a suitable" wood which is compressible, as base wood, and then upon the application of pressure through the flexible lubricated sheets of the bow the throat yields by compression, wherever necessary to make the fit perfect and the pressure uniform and thus to make the cauls together so as to provide clearance for the removal. The product at this stage, which is as wide as eight or twelve tennis rackets would be if piled upon each other, may then be sawed into strips 18 as in Figure 5, each of which has width suitable for the thickness of a single racket. From this point the processes of manufacture known to those skilled in the art of making rackets, will lead to finished articles which has the qualities above set forth.

Certain parts of the process herein described have a broader applicability. The plywood construction with longitudinal weaving of grain is useful for other articles in the nature of sticks, that is, of small cross sectional dimension but subject to severe transverse bending stresses, as sticks, clubs and runners used in hockey, golf, skiing and various other sports.

I claim as my invention:

1. A laminated 1 structure comprising a multiplicity of wood laminae with glue absorbed into and set between them; some of said laminte being of relatively strong and dense wood and other of said laminae being arranged between the strong wood laminae and being of less dence wood.

2. A laminated bow comprising a multiplicity of laminae oined rigidly together with glue, some of said laminae being of light weight material and other of them being ar-' ranged outside of the light laminae and being of material adapted better than the light material to resist wear of strings and arranged in the outer portion of the bow in position to engage the loops of the said strings.

3. A frame designed to have a minimum of weight and a maximum of transverse strength comprising laminae of two kinds of wood, the first of which kinds is stronger per unit of cross section than is the second kind, but is also heavier er said unit; and the second of which kin s is stronger per unit of weight than is the first kind.

i. A frame comprising a multiplicity of thin wood laminae, each bent to bow shape while retaining its natural cellular structure, combined with webs of glue intervening be tween each laminae and its next adjacent laminae and holding the laminae in said shape; the said laminae comprising a plurality of kinds of wood one of which kinds is relatively strong and dense per unit of volume, and another of which kinds is substantially less dense and has such greater porosity that it makes kinds, of wood, one of which kinds has a proximately the density and strength of as and another of which kinds is substantially less dense than ash and has such greater porosity that it makes a stronger joint with glue than does ash, whereby there is developed a composite bow having strength per unit of weight superior to the strength per unit of weight of the first mentioned of said kinds of wood.

Signed at Boston, Massachusetts, this third day of November, 1925.

HORACE W. HALL. 

